The present invention relates to a power switching module and a multiphase inverter equipped with the module.
In particular, the present invention relates to a power switching module comprising:                at least one power switch, i.e., at least one top power switch, placed above at least one other power switch, i.e., above at least one bottom power switch, and with each such power switch comprising upper and lower walls that are each adapted to be cooled through thermal conduction by a cooling medium, and        lower closed channels and upper closed channels configured to circulate a cooling fluid along such lower and upper walls, respectively, of such bottom and top power switches.        
Power switching modules of the above kind are used, for example, in three-phase power inverters supplying power to motors of electrical machines, such as the traction motors of a train.
Such power inverters conventionally comprise two interrupters per phase.
The currents to be switched being relatively high, for example on the order of a few thousand amperes, each interrupter is commonly formed of a plurality of power switches, each of which is in turn formed of a multitude of individual interrupters, for example insulated gate bipolar transistors (IGBT). Because of the presence of this multitude of transistors, such power interrupters are bulky and must be cooled to prevent overheating.
To this end, it is known in the art to form a power switching module in which the two interrupters of the same phase are disposed one above the other, so as to thereby reduce the overall size of the module. In such a prior art embodiment, a cooling circuit to evacuate heat generated by the transistors is formed only on the exterior surfaces of the switches of the module. Although this kind of module comprising two interrupters one above the other is less bulky than those used until now, it still has a large overall size.
Thus the invention aims to reduce even further the overall size of a power switching module comprising at least two interrupters placed one above the other.
The patent document GB 1 416 561 discloses a modular arrangement of power semiconductor components in which semiconductor elements are disposed in disc-shaped packages. A cooling liquid may circulate in a space where spring means are located between two stacked packages. This liquid cools the lower wall of the top package and the upper wall of the bottom package. Furthermore, the external walls of this modular arrangement are also cooled by a cooling liquid that circulates lengthwise of the module. Thus it is known in the art to cool a power switching module by a two-fold circulation of cooling liquid, firstly along external walls of the module and secondly inside the module. However, in the modular arrangement described in the above patent document, the spring means in the space between the two stacked packages impedes the flow of cooling liquid along the faces of the internal packages of the module and this limits thermal exchange efficiency. The overall size of the module is still large in relation to the amount of current that the module is able to switch. A relatively large quantity of cooling liquid is needed to dissipate heat via the interior faces of the components.
Thus the teaching of the above document cannot, starting with a prior art switching module in which a cooling circuit is formed exclusively on the exterior surfaces of each of the switches of the module, lead to modifying the module to reduce further its overall size, which is the aim of the invention.